A typical gasket for use in, for example, internal combustion engines comprises a base sheet that is die cut from gasket material and has one or more internal apertures surrounded by a web or webs of the gasket. As described in substantial detail in the incorporated U.S. patent application, an enhanced seal can be achieved in gaskets by forming a polymer coating on the cut interior edges that surround and bound the interior apertures of the gasket. These edge coatings can take on a variety of configurations including edge-wrapped and non edge-wrapped coatings, coatings that define raised lips surrounding internal apertures, and even coatings on exterior edges of the gaskets. Such gaskets generally are referred to herein as “edge-coated gaskets.”
While edge-coated gaskets form an improved seal as compared to traditional gaskets in a wide variety of gasketing situations, there are nevertheless some cases in which an improved seal may not be required or desired around the entire surrounding edge of a gasket aperture. For example, an adequate seal may exist with no edge coating at all in regions adjacent to bolt holes where clamping pressures on a gasket are high, while an enhanced seal still may be needed in other regions spaced from bolt holes where clamping pressures can be significantly lower. In other cases, a coating on the interior edge of a gasket may not be feasible, such as, for instance, in gaskets with relatively narrow webs. Nevertheless, an enhanced seal in certain regions of the gasket still may be needed. In still other cases, a gasket with an edge coating surrounding an interior aperture may nevertheless require an enhanced seal in other selected regions of the gasket, such as in regions of the gasket's web between widely spaced bolt holes. In these and other cases, aperture only edge-coated gaskets such as those disclosed in the incorporated disclosure are not always optimal.
In the past, attempts to provide an enhanced seal within selected regions or zones of a gasket web have included simply applying a bead of a rubber or polymer based sealant to the surface of the gasket web. The theory is that when the gasket is clamped between a pair of flanges, the bead of sealant will be compressed between the gasket web and a flange to provide an enhanced seal within the region of the gasket where the bead is located. While such solutions can be somewhat successful, they nevertheless have certain inherent problems and shortcomings. For instance, beads of sealant applied to a gasket's surface increase the effective thickness of the gasket in the region of the bead. This can result in less than optimal distribution of clamping forces when the gasket is clamped between a pair of flanges, which can degrade rather than enhance the resulting seal. Further, surface applied sealant beads generally have not been proven to provide a completely satisfactory barrier against interfacial migration of fluid across the web faces of the gasket.
Thus, a need exists for a gasket that provides an enhanced seal in selected regions or zones where additional sealing is required without the problems and shortcomings inherent in surface sealant beads and other methods used in the past to provide such selectively positioned seal enhancement zones. It is to the provision of such a gasket and a unique method of forming the gasket that the present invention is primarily directed.